Cigarette smoking is of great public health importance and is the single most important preventable cause of morbidity, mortality and excess health care costs in the United States. After a steady decline for the last 50 years, the prevalence of tobacco use in the United States has reached a plateau of approximately 21%. Currently available treatments among adults are not efficacious for all tobacco users. New pharmacologic agents thus need to be continually developed and tested. The release of dopamine in the nucleus accumbens is one of the key components of the pleasurable and rewarding effects of nicotine. Drugs that increase monoamine neurotransmitter availability (particularly dopamine and norepinephrine) are likely to increase the reward function and thus ameliorate withdrawal symptoms. S-Adenosyl-L-Methionine (SAMe), the primary methyl donor for the central nervous system (CNS), donates methyl groups towards presynaptic synthesis of CNS monoamine neurotransmitters. By facilitating the synthesis of dopamine and norepinephrine in the brain, SAMe is likely to ameliorate the symptoms of nicotine withdrawal, thus improving tobacco abstinence rates in smokers who are trying to stop smoking. SAMe is well tolerated and is available over-the-counter. To date, no prospective clinical trial evaluating the efficacy of SAMe for the treatment of tobacco dependence has been published. We propose to evaluate the efficacy of SAMe for increasing smoking abstinence and decreasing nicotine withdrawal symptoms in a randomized, blinded, placebo-controlled, three arm, parallel-group, dose-ranging phase II clinical trial. Participants (N=120) will be randomly assigned to one of the three groups, and will receive an 8-week course of SAMe 800-mg per day, 1600-mg per day, or a matching placebo. This study is anticipated to provide the data needed to develop a larger randomized controlled clinical trial submitted through the R01 funding mechanism, if the results appear promising.